This invention relates to novel and improved methods for metallizing bodies, e.g., insulating supports, and to the products which result from such methods.
More particularly, the present invention relates to imposing, by thermal or radiant energy, sensitive non-conductive metallic areas on the surfaces of such bodies which catalyze the deposition of strongly adherent and rugged deposits of electroless metal.
Although applicable whenever it is desired to apply a metallic coating to a base, as for example, for decorative or protective effects, or to make electrical conductors of a wide variety of shapes and configurations, the procedures for metallization herein are particularly useful for making printed circuits from readily available base materials, e.g., metal clad laminates, resinous insulating laminated bases or porous non-conductive materials, e.g., fiberglass, paper, cloth, cardboard, ceramics and the like.
It is a primary object of this invention to provide bases sensitive to metallization by electroless plating and, optionally, subsequent electroplated metal deposition.
Another principal object of this invention is to provide improvements in metallization processes in which a base is sensitized to metallization by electroless plating.
An additional object of this invention is to provide base materials and processes for electroless metallization in which there are employed non-noble metal sensitizers which are much more economical in cost, but equivalent in performance to the noble metal-containing sensitizers used until now.
Another object of this invention is to provide adherent electroless metal coatings bonded to base materials either directly or through an intermediate, adhesive layer.
Although the invention will be described with particular reference to printed circuits, and although fabrication of printed circuits constitutes a primary and preferred application, it should be understood that the inventon is not limited to printed circuits but is applicable to metallizing surfaces broadly.
Heretofore, it has been known to employ a number of pretreatment or sensitization baths in effecting the electroless deposition of metals on various surfaces. All such prior art sensitization baths used commercially have been expensive because they depend upon a noble metal, e.g., palladium, platinum, gold, silver, etc., as the sensitizing component. In spite of the expense, however, the prior art has stood fast in its feeling that precious metals must be used if sensitization to electroless metal deposition and good bond strength between the sensitized surface and the electroless deposit is to be achieved. In one embodiment, such prior at noble metal sensitization baths are used sequentially by providing first a film of a Group IV metal ion, e.g., stannous ion, and then a film of reduced precious metal, e.g., reduced palladium, on the surface. In another embodiment, unitary noble metal baths are used, from which there is deposited on the surface a film of colloidal noble metal or a complex of noble metal which is later reduced.
It has now been discovered that adherent electroless metal deposits can be applied to a broad variety of insulating substrates without the need to use expensive noble metals.
In addition, the methods of this invention avoid the flash deposition of precious metals which sometimes causes loss of bond strengths between the electroless metal and the base in prior art procedures.
When following the teachings herein, there can be obtained printed circuits of the highest quality using base metals only in all steps of their production.